1. Field of the Invention
The invention relates to optical communication systems, and, in particular, to optical switches implemented using micro-electro-mechanical system (MEMS) technology.
2. Description of the Related Art
Optical communication systems transmit information from source nodes to destination nodes in the form of modulated optical signals. A typical optical communication system includes a network of nodes interconnected by optical fibers. In addition to transmitting optical signals between nodes over the optical fibers, a so-called all-optical system has nodes that are able to route optical signals between input and output ports in the optical domain, i.e., without having to convert the optical signals into the electrical domain. Typical all-optical routing nodes are implemented using arrays of 1×M and M×1 optical switches to receive incoming optical signals at their corresponding input ports and present those signals as outgoing optical signals at their desired output ports.
In particular, a 1×M optical switch has a single input fiber and M output fibers. In operation, a 1×M optical switch receives an optical signal from the input fiber and selectively routes that optical signal to one (and only one) of the M output fibers. Similarly, an M×1 optical switch has M input fibers and a single output fiber. In operation, an M×1 optical switch selectively receives an optical signal from one of the M input fibers and routes (only) that optical signal to the output fiber.
A 1×M or M×1 optical switch, where M>2, may be implemented using a cascade of 1×2 or 2×1 optical switches. For example, a 1×8 optical switch may be implemented using three levels of 1×2 switches: one 1×2 switch in a first level feeding two 1×2 switches in a second level, each feeding two of four 1×2 switches in a third level. By appropriately controlling the seven different switches, an optical signal received at the first-level switch can be routed to any one of the eight outputs of the four third-level switches.
One type of prior art 1×2 optical switch is a mechanical device that changes the direction of its received light between two outputs by mechanically inserting or removing an optical prism into or from the light path. Unfortunately, such mechanical devices have poor reliability, especially at higher switching speeds (i.e., the speed at which the configuration of a 1×2 switch can be changed from one output to another).